This invention relates to an instrument for sensing angular velocity about two non-parallel axes, and more particularly to an improved angular velocity sensor having a gas damped inertial element.
Two axis angular rate of turn devices are known which utilize one spinning gyroscopic element having a spin axis which is caused to move away from a neutral orientation by precessional torque resulting from angular rate inputs about either of two orthogonal input axes. Some means of restraining the precession of the gyroscopic element is employed, such as a linear spring, so that the degree of precession may be sensed to thereby provide a signal corresponding to the angular velocity about each of the two input axes. Attempts in the past to obtain such dual axes angular velocity sensors have resulted in highly complex structure and highly sophisticated technology resulting in considerable cost figures. One such sensor utilizes a rotating shaft and rotor flexure suspension that may be visualized as a "ball and socket" joint between the shaft case and rotor. The flexure suspension has radial and axial rigidity, but low compliance for bending about axes normal to the spin axis. Such an instrument is described in conjunction with FIG. 2 in Control Engineering, Page 54 through 58, "Reviewing the Status of Inertial Sensors," March, 1971.
Another type of flexure supported gyroscope has only a single degree of freedom flexure between the rotating structure and the rotational drive shaft. Two axes of angular velocity are measured by measuring case to rotor displacement at orthogonal positions on the case. Such a sensor is described in conjunction with FIG. 3 of the Control Engineering article above. A two axis rate gyro is described in U.S. Pat. No. 3,176,523 to Amlie which has a static spring with radial and axial rigidity and low compliance for bending to allow restrained rotation of a gyroscopic element due to precessional torque, U.S. Pat. No. 3,559,492 to Erdley describes a two axis angular rate sensor having a rotating assembly including a multiplicity of peripheral vibrating elements mounted on radial torsion springs, whereby individual ones of the peripheral elements vibrate torsionally independent of the others.
The assignee of the invention disclosed herein also owns an invention wherein the inertial element is a thin plate-like rotor having the capability of bending about any axis and providing a spring rate restraining such bending when imposed on the rotor by precessional torque. An improved two axis angular velocity sensor is needed having relatively simple constructional features, low spring restraint providing strong structural support, easily obtained damping so that performance approaches that of a linear second order system, and two axis output signal discrimination.